In recent years, environmental problems such as leachate leaking from various kinds of garbage generated along with the development of industry and penetrating into the underground, polluted air falling along with rainwater and penetrating into the underground, and pollution of water, are damaging to human healthy life.
In order to solve the environmental problems caused by water pollution, various solutions such as recycling of wastewater, purification of drinking water for household use, treatment of chemical substances and so on have been searched, and a multifaceted research on a liquid treatment filter for substantially purifying contaminated water has been conducted.
The liquid treatment filter is divided into a simple filtration treatment and an adsorptive filtration treatment. Depending on the direction of the liquid flowing into the filter, the filter may be divided into a downflow system that flows from the upper portion of the filter to the lower portion thereof and an upflow system that flows from the lower portion of the filter to the upper portion thereof, and depending on the pressure, the filter may be classified into a gravity type and a pressure type.
Cartridge-type liquid filters, which are kinds of the liquid treatment filters, have been increasingly used because of their high utility in domestic and industrial applications, but excellent performance capable of removing various microorganisms, various heavy metals and chemicals contained in liquids with high efficiency is desperately required.
Meanwhile, a membrane is used as a separation membrane of a liquid treatment filter, and serves to filter other impurities in the water through a membrane film.
Polymer membranes, which are a kind of such membranes, are prepared by forming a polymer solution by selecting a suitable polymer and a solvent, casting the polymer solution into a thin sheet, and depositing the same in solid-phase and used as a liquid filtration use.
Korean Patent Application Publication No. 10-2011-0005479 discloses a cylindrical cartridge filter comprising: a deep layer portion which is an inner core without a support while applying heat by using a polypropylene melt-blown nonwoven web and a polypropylene/polyethylene sheeting nonwoven web of medium density having a porosity of 20% to 40%; an intermediate layer portion having excellent particle removal performance while applying heat by using a nonwoven nano-web and a polypropylene/polyethylene sheeting nonwoven web of high density having a porosity of 10% to 30%; and an outer layer portion while applying heat by using a polypropylene melt-blown nonwoven web and a polypropylene/polyethylene sheeting nonwoven web of low density having a porosity of 40% to 60%. Korean Patent Application Publication No. 10-2011-0005479 has an excellent strength and a smooth flow of purified water by the nonwoven web. However, since the pore size of the nonwoven fabrics is large, ultrafine-sized foreign matters and ionic foreign substances cannot be filtered.
Korean Patent Application Publication No. 10-2012-0077266 discloses a filtering membrane comprising: a porous support including a porous nonwoven substrate composed of a thermoplastic polymer nanofiber aggregate having a fineness of 50 μm or less and having a pore size of 0.002 μm to 3 μm after being cross-linked with the polymer nanofiber aggregate; and an asymmetric membrane deposited on the porous support. However, in such a filtering membrane, the porous support is a nonwoven web having a porous property while maintaining the strength thereof, and the asymmetric membrane is a reverse osmosis membrane that allows water to pass through but not allow ions to pass therethrough. Thus, the filtering membrane performs only the function of filtering particles included in the water and larger than the pore size with the nonwoven web alone. As a result, a layered reverse osmosis membrane is required to filter ions.
Therefore, the filtering membrane disclosed in Korean Patent Application Publication No. 10-2012-0077266 is thick and requires a lot of manufacturing cost, and is not excellent in hydrophilicity and has a limitation in increasing the flow rate.